Ok , I've pretty much solved my wheel well woes, which were two fold.
1. the original builder didn't cover the foam insulation in the walls, under the wheel wells. So the foam insulation was exposed to the sticks and stones, rain, ice and snow (road salt) and it didn't fair well. So I chose to get a 1" think piece of plywood. Seal it to extremes (poly and caulk) then mount it in the wheel wells behind the tire to seal in the wall insulation. (I had tried to seal all the walls with caulk, which worked everywhere but the wheel well where there was nothing outside to hold the wall in, and the caulk to the wall...






2. Part two which was more agonizing to fix yet took only a few minutes to resolve once I finally figured it out.
My ST78R-13's were too large and rubbing the wheel well at maxed out loading and bumps. No smaller circumference 13" tires are readily available. Even the 12"ers are not common to regular tire centers. So to go with "I want tires readily available and to hold a great load" I had to do something about the wheel well rubbing. Well the start of the fix was, take a hacksaw to the wheel well and "flair it" where it was rubbing, which turned out to only be the backs. If that doesn't do it then I'll put in heavier leaf springs. This way I have easy to replace, heavy hauling tires. (I even repacked my bearing while I was in there. Been a while since I done those. Fun-greasey! :-) AS you can see below, I went a few inches beyond where the rubbing was occurring, with the cut and flair. The cut is as close to the outer wall of vinyl siding I could get.


might not notice if I didn't point it out. some smoothing to go but ready for a field test.
maybe some mud flaps.
:-)